The present invention relates to four engine VTOL aircraft.
A roll control problem arises in tilt fan VTOL aircraft when an engine fails. Military VTOL aircraft are required to maintain control in the event of sudden failure of an engine during takeoff or landing. They are required to maintain hover only at the considerably lighter landing condition. The Grumman 698 Tilt Fan design was able to meet military requirements with two engines with their fans cross-shafted to each other.
When there is an engine failure in a civil transport aircraft, where controlled hover must be maintained at the takeoff gross weight, twin engine designs with good payload/fuel loss are not possible. A four engine design is required where only one fourth of the installed power is lost upon engine failure as opposed to a one half power loss upon engine failure in twin engine aircraft. The added complexity of the extra two engines of a four engine aircraft is the penalty paid for a viable civil VTOL design. In a known four engine design, all four engines are moved laterally to achieve rolling moment balance. Although this system is mechanically feasible, it is likely to be heavy and considered complex. The four engine design can forego the complex and heavy cross-shaft of the twin engine design, however, if engine-failure roll control can be maintained.
The principal object of the invention is to provide a four engine VTOL aircraft having roll control upon failure of an engine.
An object of the invention is to provide a four engine VTOL aircraft having a roll control of simple structure which comes into operation upon failure of an engine.
Another object of the invention is to provide a four engine VTOL aircraft having efficient and reliable roll control effective upon failure of an engine.
Still another object of the invention is to provide a four engine VTOL aircraft having a roll control of simple structure which is built into the aircraft with facility and convenience and functions efficiently and reliably to control roll upon failure of an engine.